Cold rolling profiles on cylindrical workpieces

ABSTRACT

In a method for cold rolling profiles on the circumference of a rotating cylindrical workpiece, using tool worms of appropriate profile, the worms performing generating motions corresponding to the profile required in successive part-rolling operations by being moved relative to the workpiece in a closed-circuit locus path having one axis which is in the direction of and smaller than the tooth depth, and which substantially smaller than another axis of said locus which is in the direction of tooth length or thickness, with each part-rolling operation being performed over the entire tooth facewidth while the tools are retained, over the workpiece width, in their dead center position which is a position on said locus innermost relative to the axis of the workpiece, the profile being preformed by progressive radial feed of the operating stroke of the tools and with a number of enveloping planes, and the profile being subsequently, finish-formed with a larger number of enveloping planes and with an unchanged inner dead center position of the tool worms.

United States Patent [1 1 Meyer et a].

[111 3,713,315 Jan. 30, 1973 [541 COLD ROLLING PROFILES 0N CYLINDRICALWORKPIECES [75] Inventors: Albert Meyer, Thalwil; Otto Wenger; OskarMaag, both of Zurich, all of Switzerland [52] U.S. Cl. ..72/l00, 72/95,72/104 [51] Int. Cl. ..B2lh 5/02 [58] Field of Search ..72/95, 100, 101,102, 103,

[56] References Cited UNITED STATES PATENTS 2,991,672 7/l96l Meyer etal. ..72/l00 3,032,871 5/1962 Meyer et al.

3,159,062 l2/l964 Goodwill Inn/103 Primary Examiner-Lowell A. LarsonAttorney-McGlew and Toren [57] ABSTRACT In a method for cold rollingprofiles on the circumference of a rotating cylindrical workpiece, usingtoo] worms of appropriate profile, the worms performing generatingmotions corresponding to the profile required in successive part-rollingoperations by being moved relative to the workpiece in a closed-circuitlocus path having one axis which is in the direction of and smaller thanthe tooth depth, and which substantially smaller than another axis ofsaid locus which is in the direction of tooth length or thickness, witheach part-rolling operation being performed over the entire toothfacewidth while the tools are retained, over the workpiece width, intheir dead center position which is a position on said locus innermostrelative to the axis of the workpiece, the profile being preformed byprogressive radial feed of the operating stroke of the tools and with anumber of enveloping planes, and the profile being subsequently,finish-formed with a larger number of enveloping planes and with anunchanged inner dead center position of the tool worms.

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p 3.713.315 I SHEETBUF7 JNVE NTo RS ALBERT MEYER orro wauesa osxm HMSATTORNEYS COLD ROLLING PROFILES ON CYLINDRICAL WORKPIECES The inventionrelates to a method for the cold rolling of a gear tooth profile on thecircumference of a cylindrical work piece, and to a machine forperforming the said method.

A known machine for the cold rolling of gearwheel teeth employsworm-shaped profiling tools having the reference profile, and beingadapted to perform generating motions relative to the rotationallydriven workpiece and in accordance with the profile to be generated, andperforming successive part-rolling operations on the workpiece by beingmoved relative to the workpiece on a closed-circuit locus having oneaxis which is in the direction of and smaller than the tooth depth andwhich is substantially smaller than another axis of said locus which isin the direction of the tooth length or thickness. The tools move in anelliptiform path (the said closed-circuit locus) which has a minor axisand a major axis, the extremities of the minor axis being dead centerpositions, the inner dead center position being that which is nearer theaxis of the workpiece. The inner dead center position is defined by thetooth root of the gear which is to be generated. During each partrolling operation the tool is first moved relative to the workpiece inthe position which is radially the lowest with respect to the workpiece,and at the end of its stroke, which is axial relative to the workpiecethe tool is lifted from the rolled gap, to continue in theclosed-circuit locus, the said tool being gradually fed axially forward,between successive locus circuits, during the continuous part-rollingoperations of tools. In each part-rolling the profiling tools will firstfinishform the profile already prerolled and at the end of their motion,while the tools are radially retracted, an axially adjoining part of theprofile will be preformed. In order to obtain the desired quality ofgearing, finish-forming of the tooth with the reference profile must beperformed with a plurality of; enveloping planes, that is, the imaginaryplanes swept by the flanks of the tool worm teeth, producing (in thepreforming stage) visible flats on the gear teeth; however,-a smallernumber of enveloping planes would be sufficient for the preforming ofthe tooth. However, since preforming of one portion of the profile andfinish-forming of another portion of the profile have to be performed inone and the same operation, it follows that the speed at which theprofile is produced is defined by the part rolling operations requiredfor finish forming.

It is the object of the invention to provide an improved method andapparatus by means of which the manufacturing speed in cold rolling ofgearwheel profiles on the circumference of a cylindrical workpiece canbe substantially increased.

According to the invention, the rolling is effected in a plurality ofpart-rolling operations, each part-rolling operation, is performed overtheentire tooth facewidth with the tool worms being retained, at leastover the tooth facewidth, in an inner dead center position, ashereinbefore defined,'in said locus, said plurality of operationsincluding preforming the tooth profilein a number of enveloping planesby progressive feed toward the workpiece of the operating stroke of thetool worms in the radial direction of the tool worm and workpiecebetween successive complete movements in said closed-circuit locus, andfinish-forming said profile in a larger number of enveloping planes,each envelop- -ing plane being accomplished with the tool worms retainedin a said inner dead center position.

Since preforming and finish-forming take place successively it ispossible for the feed motion for preforming to be executed withoutreference to the finish-forming of the profile. In selecting thematerial volume to be deformed in each rolling stroke during thepreforming operation it is merely necessary for the appropriate choiceto be made in accordance with the material to be deformed. A smallnumber of enveloping planes are sufficient for rough preforming whilethe required accuracy of gearing is obtained in finish-forming with alarger number of enveloping planes.

it is particularly advantageous if each part-rolling operation is alwaysperformed with the same position of the profile of the tool wormsrelative to the workpiece so that the tooth profile is formed over itsentire length with the same enveloping planes, each enveloping planehaving the same position relative to the tooth gap being formed.

In an appropriate embodiment, preforming is performed with'between 1.5and 2.5, but preferably with 2, part-rolling operations for eachrotation of the tool worms while the ratio of part-rolling operationsfor each tool worm rotation selected for finish-forming is smaller orlarger by a small amount, said ratio being exactly a figure no smallerthan a high multiple of the number of teeth on the workpiece. If theprofile is produced by means of two part-rolling operations for eachrotation of the tool worms, the tooth profile will be preformed withthree enveloping planes which are generally sufficient to closelyapproach the involute tooth profile. Finish-forming is then performedwith a larger number of enveloping planes.

A machine for carrying out the said method, provided with tool wormswhich are adjustable at an angle and are supported in tool supportswhich are radially movable and axially reciprocable relative to theworkpiece, and having a rotary drive for the tool worm and for theworkpiece to impart to both the tool worms and the workpiece a relativegenerating motion which corresponds to the profile to be generated, ischaracterized in that the tool supports can be reciprocated exclusivelyin the direction which is radial relative to the workpiece axis and thatthe workpiece is supported in a work slide which can be reciprocated inparallel to the workpiece axis over more than the facewidth of thegeartooth being formed on the workpiece and that the rotational drive of theworkpiece spindle is provided through an interchangeable lead bush toproduce the desired rotation of the workpiece.

To ensure that the tool worm and the workpiece retain their relativeposition to each other when each part-rolling operation is performed, afirst angularly adjustable slotted link is preferably mounted on thework slide and ,is adapted, duringeach stroke of the work slide, toaxially displace a driving wormfor imparting rotation to the workpiecein order to counteract the inherent generating action of the workpieceduring each part-rolling motion, a second angularly-adjustable slottedlink being provided to axially displace the tool worms during eachstroke of the work slide in order to worms during each part-rollingmotion.

During the part-rolling motion, the axial stroke of the workpiece shouldbe performed at a constant velocity which should correspond to therolling velocity of the tool worms so that wear thereof is minimized. Inthe machine according ,to the invention this problem is solved in that acrank with a crank rocker, a connecting rod and a two-armed lever areprovided for. reciprocating the work slide and are so disposed that thesinusoidal oscillation of the rocker crank is converted into an axialreciprocation of the work slide so that the work slide moves at constantvelocity.

The method according to the invention, and a machine-for performing themethod, are disclosed in the following description of an embodiment of amachine for the cold rolling of gear profiles, and shown in theaccompanying drawings, wherein:

FIG. 1 is a vertical section along the workpiece axis and on the line1--1 of FIG. 2;

FIG. 2 is a vertical section on the line 11-11 of FIG. 1, only one toolsupport with its drive being shown;

FIG. 3 is a part end elevation, looking in the direction of arrow 111 ofFIG. 2;

FIG. 4 is a horizontal section along the line of IV-IV of FIG. 5,through a workpiece and tool worms during the; finish-forming of theprofile in a cold rolling of a straight-tooth spur gear;

FIG. 5 is a vertical. section along the line Y-Y of FIG. 4 during thefinish forming of a workpiece having an even number of teeth;

FIG. 6 is a vertical section similar to FIG. 5 during the finish-formingof a workpiece having an odd number of teeth;

FIG. 7 shows the path of a tool worm in relation to a workpiece assumedto be stationary when the tool worm forms the tooth root;

FIGS. 8 and 9 show the conditions of the tool worm relative to theworkpiece, the ratio of the number of strokes of the workpiece for eachtool worm rotation being K 2;

FIG. 10 shows an enlarged cross-section through a tooth of theworkpiece; I

FIG. 11 is a plan view of the workpiece and tool worms during the coldrolling of a helical gear;

FIG. l2-is a view corresponding to FIG. 7 but showing the cold rollingof teeth with longitudinal crowning; and

FIG. 13 is a view corresponding to FIG. 12, showing the simultaneouscoldrolling of two gearwheels with longitudinally-crowned teeth.

In the machine illustrated in FIG. 1 to 3 for cold rolling helical gearon the circumference of a cylindrical workpiece, the said cylindricalworkpiece 1 is retained, as shown in FIG. 1, atone of its ends by meansof a clamping device 2 of a work spindle 3 journaled in aspindle-bearing pedestal 4 at the end, the left-hand end in FIG. 1, of ayoke-shaped work slide 5. At its other end the workpiece 1 is supportedin the work slide 5 by means ofa work holder 6 having a mandrel 7. Thework slide 5 is slidably guided by V-shaped guide surfaces 8 thereonsliding in corresponding guide surfaces 9 in a machine frame 10, saidguide surfaces 8 being disposed on both sides of the workpiece andextending in parallel to the axis X thereof.

A lead bush 11, having helical guide grooves 12 of a lead approximatelyequal to the leadof the gear tooth helix, is flange-mounted on the endof 'the work spindle 3 remote from the workpiece. Sliding blocks 13,disposed in the interior of a driver collar 14, co-operate with theguide grooves 12, the drive collar 14' being mounted on the end face ofthe hollow boss 15 of a wormwheel 16 which is immovable axially but isrotatably journalled in the machine frame 10. By virtue of thisarrangement, a reciprocating motion of the work slide 5 imparts to theworkpiece a rotating motion cor responding to the desired helix angle ofthe profile which is to be generated. The lead'bush 11 together with theassociated driver collar 14 is interchangeable.

The work slide 5 is causedto move axially of the workpiece I by a crankrocker 20 through a doublearmed lever 18, hinged on said work slide bymeans of a bolt 17, and a connecting rod 19. The crank rocker 20 iscaused to reciprocate, on an axle bolt 21 supported in theframe 10, by acrank 22 (FIG. 2) the crank pin 23 of which carries a sliding block 24which is guided in a longitudinal guide 25 in the crank rocker 20. Thecrank 22 is disposed at one end of a shaft 26 which is driven from amain shaft 29 of the machine through a gearwheel pair 27, 28, the saidmain shaft in turn receiving its drive from a motor 31 through a belt30. The sinusoidal oscillation of the crank rocker 20 obtained from thecrank 22 is converted into an axial reciprocating motion of the workslide 5 by an appropriate choice of the dimensions of the doublearmedlever 18, the connecting rod 19 and the crank rocker 20 whereby themotion of the work slide 5 to the right'(FIG. l) is extended so as to beperformed practically at constant velocity. Accordingly, the workpiece 1is moved axially practically at constant velocity during its motion tothe right during which, as will be described later, partial rollingoperations are performed thereon.

The double-armed lever 18 contains a guide slot 32 in which a slottedlink 34 is guided, said slotted link accommodating a pivot pin 33. Thepivot pin 33 is mounted on a bracket 35 which slides in a guide 36 onthe frame 10 in a direction which is radial relative to the workpieceaxis X, said bracket being adjustable by means of a spindle 37 and aworm drive 38 so that displacement of the pivoting pin 33 of thedouble-armed lever 18 enables the length and therefore the velocity ofthe axial motion of the work slide to be adjusted.

The profiling tools 40 take the form of worms (hereinafter referred toas tool worms) of which the normal section through the threads has thebasic rack profile of the gear being rolled. In the illustrated machine,and as shown inv FIG. 4, two tool worms are provided and are disposeddiametrically opposite each other, FIG. -2 showing only one of the toolworms 40 together with its drive.

The trunnions 41 of a tool worm 40 are rotatably supported in a toolhead42. The tool head is supported by means of ,a circular guide 43 on atool carrier 44 so as to be angularly adjustable about an axis Y whichin tersects the workpiece axis and the axis of the tool worm 40 at rightangles. For'the sake of simplicity, the tool head 42 in FIG. 2 is shownso adjusted that the axis of the tool worm 40 is disposed in the planeof the drawing. When straight teeth are cold rolled, the axis of thetool worm 40 will of course be inclined relative to the said plane atanangle similar to the pitch angle of the screw thread of the tool worm.

The tool carrier 44 is guided in a guide 45 of the machine frame alongthe said axis Y. An annular piston 48, constantly biased, by means ofone of the branches of an oil distribution network 49 from a pressuresource 50, in the direction of lift-off of the tool worm from theworkpiece 1, is provided on a rearward extension 46, of smallerdiameter, of the tool carrier 44, the extension 46 being guided in abore 47 in the machine frame.

The rearward extension 46 of the tool carrier 44 extends through anopening 51 in a wedge 52 whose rear inclined wedge surface 53 issupported on a correspondingly inclined guide surface 54 in the machineframe, and whose front surface 55 is disposed at right angles to theaxis Y and bears on the end face of a nut 56 for the feed of the toolworm 40, the said nut cooperating with screwthreading 57 on the externalsurface of a shoulder 58 on the rearward extension 46 of the toolcarrier 44. The external circumference of the feed nut 56 is providedwith worm wheel gearing 59 and can be rotated by means of a worm 60 froma control drive 61 for controlling the feed motion of the tool worm.

The oil pressure acting on the annular piston 48 ensures that the toolsupport 44 is constantly thrust by the feed nut56 against the wedge 52.

A piston 62, slidable in a cylinder bore 63, which is biased by the oilpressure of the coil pressure supply network 49, thrusts on the broadend of the wedge 52. The piston 62 retains the narrow end of the wedge52 constantly in physical contact with a tappet 64 which in turn bearson a tappet roller 65', supported on'one arm 66 of a rocker lever, theother arm 67 of which cooperates through a cam'follower' roller 68 witha disc cam 69 which is mounted on a shaft 70 driven through a bevel gearpair 71, 72 from the shaft 26.

Rotation of the disc cam 69' is accompanied by reciprocation of thewedge 52 and therefore by reciprocation of the tool carrier 44 with thetool head 42 and the tool worm 40. A connecting rod 73, hinged on theend of the arm 67 of the rocker lever 66, 67, and connected with acorresponding rocker lever of the reciprocating drive of the second toolworm, not shown ensures that the latter performs the same reciprocatingmotions.

Reciprocation of the workpiece l in the direction of the axis X and ofthe tool slide 40 in the direction of the axis Y both derive from thesame shaft 26 and therefore are in synchronism with each other, and arelative generating motion, corresponding to the profile to begenerated, is imparted to both the tool worm and the workpiece.

To perform the generatingmotion, the workpiece 1 is rotated by the mainshaft 29. As can be seen in FIG. 1, the main shaft 29 drives, through abevel drive 74, a

on a shaft 91. The control member of a dog clutch 92 is slidably mountedon the shaft 91 and can be optionally engaged with the dogs of awormwheel 94, rotatable in the machine frame 10 by an adjusting worm 93,in order to couple the shaft 91 to the wormwheel 94, or may be engagedwith dogs on the gearwheel in order to couple the shaft 91 to thegearwheel 90. In the latter case, a supplementary rotating motion isimparted to the planet gear cage 97 of the differential transmission 77,and therefore to the output shaft 98 of the said differentialtransmission, through the toothed belt drive 89, 90, the shaft 91, achange gear set and a pinion '96, while in the former case the planetgear cage 97 is retained motionless by means of the dog clutch 92. Thepartial change gear set 83 is defined by the desired number of teeth ofthe gearing to be produced on the circumference of the workpiece 1. Thepurpose of the two change gear sets 78 and 95 will be describedsubsequently.

To rotate the tool worms 40, a shaft 99, disposed in the drive line forthe workpiece 1 and having mounted thereon the last wheel of the changegear transmission 78 and the gearwheel 79, is extended and drives,through a bevel drive 100, a shaft 101(FIG. 2) from which rotation ofboth tools is derived.

At each end the shaft 101 is provided with one pinion 102 of an axiallyslidable toothed belt drive 103 which in turn drives a shaft 104,journaled on the geometrical reduction shaft 75, a gear wheel pair 76, adifferential transmission 77, a change gear set 78, gearwheels 79,

8 0, 81, a partial change gear set 83, a bevel drive 84 and a gearwheelpair 85, 86, a worm 87 which meshes with the wormwheel 16 which in turndrives the'work' axis Y in the tool support 44. The aforementioned shaft104 in turn drives," through a bevel drive 105, a gearwheel 106 whichmeshes, by way of an intermediate wheel 107, with a gearwheel 108provided on the lower trunnion 41 of a tool worm 40.

The reciprocating-drive for the work slide 5 and the reciprocating drivefor the tool support 44'are matched to each other so that the tool worms40 assume their inner dead center position relative to the workpieceaxis X (FIGS. 1 and 2) when the work slide 5 is moved to the right inFIG. 1. This motion is therefore accompanied bythe part rolling motionsof the tool 'worms 40 on the workpiece. It is desirable that the profileof the worm thread of each tool worm 40 retains its position unchangedduring each part rolling operation relative to the tooth gap-to berolled into the workpiece 1. To

this end the tendency, because of the rotation each tool worm 40, ofthepoints of contact between the worm tooth flanks and the workpiece toothflanks to wander off-center towards the left or right (FIGS. 5,6,8 and9) and, as'a result, up or down between tooth tip and tooth root (whichproduces the action known as inherent generating action) is counteractedby axialdisplacement'of the tool worm and by movement of the workpieceslide 5'to the right.

Means for obtaining compensation of the tool worm rotation during themotion of the work slide 5 to the right will now be described.

The trunion 41 of the tool worm 40, at the top in FIG. 2, is journaledina cylindrical bore 109, closed at one end, into which a branch of theoil pressure distribution network 49'extends, so that the end'face ofthe aforementioned trunnion 41' is constantly biased with oil pressure.Accordingly, the tool worm 40 is retained by means of a thrustbearing110 in contact with a tappet l 11 whose rear end bears by way of aneedle bearing 112, on a wedge 113 which'is adapted to reciprocated inthe tool head 42.

The reciprocating motion of the wedge 113 of each of the two tool worms40 is directly derived from the motion of the workslidc 5.To this end,the underside of the work slide is provided with an angularly-adjustableslotted link 114 with a slotted link guide 115 (FIG. 1). The slottedlink114 may be adjusted angularly by an adjusting worm 116 and may beretained in the selected position by means of a locking nut 117. Asliding block 118 slides in the slotted link guide 115 and is supportedon a pin 120 which extends upwardly from a slide 119. Theslide 119 issupported in a guide 121 in the machine frame 10 and extends at rightangles to the workpiece axis X. Each end of the slide 119 has joined toit one end of a connecting rod 122 for the reciprocating drive of thewedges 113 of both tool worms 40. At its other end, each connecting rod122 is hinged to one end of a double-armed lever 123, the other end ofwhich lever is connected by a connecting rod 124 to one end of adouble-armed lever 125 supported in the tool head 42, the connecting rod124 extending along the axis Y of the tool carrier 144 and through alongitudinal bore in the shaft 104, the other end of the double-armedlever 125 being adapted to move the wedge 113. To prevent thereciprocating motion of the tool carrier 44 from affecting thereciprocating motion of the wedge 113,the double-armed lever 123 issupported, as shown in FIG. 3, on a pivoting pin 126 the ends of whichare supported in double-armed levers 127 which are always of the samelength as the lever 123, one of the ends of each lever 127 beingpivotally mounted in bosses 128 on the rearward end of the tool carrierextension 46, while the other end of each double-lever 127 is guided, bya pivot pin having a head 129 providing a sliding block, in a slottedlink guide 130 in the machine frame 10.

The apparatus by means of which the inherent generating action on theworkpiece l is counteracted during the motion of the work slide 5 to theright, is disclosed in FIG. 1.

A slotted link 131, angularly adjustable by means of an adjusting screw132 around a horizontal axis and at an angle relative to the workpieceaxis X, is supported on a bracket n the spindle-bearing pedestal 4. Ablock 134, in which a pin on one end ofa double-armed lever 135 isjournaled, slides in a guide 133 in the slotted link 131. Thedouble-armed lever 135 pivots about an eccentric bearing pin 136 on ashaft 137 which is supported in a bracket 138 of the machine frame. Theother end of the double-armed lever 135 is formed into a clevis 139 fromwhich two trunnions extend inwardly into an annular groove 140 betweentwo collars on the shaft of the worm 87 which is adapted to rotate thework spindle 3.

When the slotted link 131 is adjusted as illustrated in FIG. 1, a motionof the work slide to theright causes the double-armed lever 135 to bepivoted in the anticlockwise direction and the worm 87, constantly It ishowever not necessary for a separate lead bush 11 to be provided for anyhelix angle that may be encountered. A few lead bushes with graded pitchangles of the guide groove 12 are sufficient; for a desired and definedhelix angle the lead bush 11 with the associated driver collar is fittedinto the machine, the guide groove 12 having the pitch angle nearest tothe desired helix angle. The desired helix angle may then be obtained bycorresponding additional adjustment on the slotted link 131 which is setup so that the worm wheel 16 does not remain stationary when the workslide 5 moves to the right but experiences the required smallsupplementary rotation or reverse rotation which is necessary to obtainfor the. gear tooth system of the workpiece l the helix angle which isslightly larger or smaller relative to the pitch of the guide grooves 12of the lead bush 11.

It is of course also necessary for the crossing angle of the axis of thetool worm 40 relative to the workpiece axis X to be adjusted inaccordance with the helix angle of the gear tooth system of begenerated. This setting is obtained in that the tool head 42 is adjustedby its circular guide 43 to the corresponding angle relative to theworkpiece axis X by means of a control drive 141 through a worm 142which meshes with worm gearing 143 formed on the circumference of thetool head.

It may be assumed that a straight-tooth spur gear is to be produced withthe machine described hereinabove. To this end, a cylindrical member,the external diameter corresponding approximately to the pitch circlediameter of the gearwheel to be generated, is connected to the workspindle 3 by means of the clamping device 2 into which the saidworkpiece is thrust by the work holder 6. Since straight-tooth gearingis to be obtained, the tool head 42 isadjusted, by the control drive141,'relative to the tool support 44 so that the axis of the tool worm40 intersects with the workpiece Axis X at the pitch angle of the toolworm. When the tool carrier 44 assumes its inner dead center positionthe feed of the tool worms 40 relative to the workpiece is obtained byvirtue of the fact that the feed nut 56 is rotated by the control drive61, by way of the worm drive 60, 59, until the external diameter of thetool worm 40 is just clear of the workpiece I.

Also, when the tool support 44 is in the inner dead center position, thetool worms 40 have their screw threads adjusted symmetrically relativeto the workpiece axis X, namely by rotation of the worm 93 when the dogclutch 92 is coupled to the wormwheel 94. Since the input shaft 88 ofthe differential transmission 77 is stationary when the motor isswitched off, rotation of the adjusting screw 93 of the planet wheelcage 97,

and therefore the output shaft 98 0f the differential transmission,causes the tool worms 40 to be rotated through the earlier-describedsupplementary rotation until the desired symmetrical position relativeto the workpiece is obtained.

The position of symmetry of the tool worms 40 relative to the workpieceaxis X for a workpiece wheel 1 with an even number of teeth is shown inFIG. 5 in which, in the interests of simplification, the axes of thetool worms are shown tipped into the plane of the drawing. In actualfact, however, in the case of a workpiece wheel 1 with straight teeth,the axes would pass through the plane of the drawing at an angle equalto the pitch angle of the worm thread. In this position of symmetry, thecenter lines of the two diametrically opposed sections through the wormthreads of thetwo tool worms coincide in a section extending along theplane which is normal to the workpiece axis X and with the shortestconnecting line between the said axes which intersect the workpiece axisand the-axes of the tool worms at right angles.

FIG. 6 shows the position of symmetry of the tool worms with an oddnumber of teeth of the workpiece wheel 1. In this case, one tool worm isrotated through 180 relative to its position in FIG. so that in thenormal section to the workpiece axis X described herein, the'worm threadof one tool worm is disposed diametrically opposite to the gap betweentwo adjacent turns of the worm thread of the other tool worm.

When the tool worms act on the workpiece in the position of symmetry,the pressures exerted by each tool worm on the workpiece are alreadyautomatically compensated on each tool worm with respect to thetangential components and the radial pressures are. eliminated by virtueof the fact that the tool worms are disposed diametrically opposite eachother.

The motor 31 is started after the pivot pin 33 of the double-armed lever18 is adjusted by the worm drive 38 and the spindle 37 so that the axialmotion of'the work slide 5 is greater than the tooth width of theworkpiece 1 and after the work slide velocity during the righthandmotion is set, in accordance with calculations, to correspond totherolling speed of the tool worms. Accordingly, and by means of thecrank 22, the work slide 5 is axially reciprocated in the direction ofthe workpiece axis X and, by means of the disc cam 69, the tool 4supports 44 are reciprocated by the wedges 52 in synchronism and in thedirection of the axis Y. The disc cam 69 is so constructed that the toolworms 40 obtain and retain their inner dead center position when thework slide in FIG. 1 moves to the right. The path traversed by the toolworms 40 relative to the workpiece 1 (a closed-circuit locus),designated with the numeral 144 in FIG. 7, results from the synchronizedreciprocating motion between the workpiece and the tool worms.

During the reciprocating motion of the workpiece and the tool worm, bothare rotated by the abovedescribed rotary drive so that an inherentgenerating action, corresponding to the profile to be generated, isobtained between the tool worms and the workpiece, but this inherentgenerating action is counteracted by the above-describedcounter-generating apparatus, operating in synchronism with the workslide motion, namely the apparatus for the axial displacement of thetool worms 40 and the apparatus for the axial displacement of thedriving worm 87, such compensation taking place during the time in whichthe tool worms 40 are disposed in their inner dead-center position andwhen the work slide acts to the right upon the workpiece 1.

For preforming, the tool worms 40 are gradually, or in steps, advancedby means of their associated control drive 61 towards the workpiece axisX until the tooth profile is rolled from the workpiece over its fullheight. 7

approximately the same workpiece volume is displaced with eachpart-rolling operation.

When the workpiece gearing is being preformed, the dog clutch 92 isengaged with the dogs of the worm wheel 94 which is retained in positionby the adjusting worm 93. The dog clutch retains the shaft 91 andtherefore the planet wheel cage 97 of the differential transmissionthrough the change gear set 95 and the pinion 96. The gearing ispreformed with a few enveloping planes. For example it may be assumedthat the change gear set 78 is so selected that for each rotation ofvthe tool worm 40, and therefore one tooth pitch on the gearing to begenerated, the work slide 5 performs two strokes and the ratio ofworkpiece strokes per tool rotation is K 2. The two positions assumed byeach tool worm in the two stokes and relative to the workpiece areillustrated in FIGS. 8 and 9 which represent the engagement of the toolworm and workpiece at the end of the preforming operation. In FIG. 8 inthe middle of one tool tooth is opposite to the middle .of a tooth gapof the workpiece. One tool tooth forms the tooth root of the tooth gapwhile the two adjacent tool teeth form the tip of the tooth profile ofthe two workpiece teeth adjacent to the gap. In FIG. 9 a tooth gap onthe tool is disposed opposite to a tooth on the workpiece. In thisconfiguration the middle zones of the two flanks of the workpiece toothare formed.FlG. 10 shows a cross-section through a tooth of theworkpiece wheel 1 in greatly enlarged form. The line 145 indicates theprofile of the tooth which is not yet preformed over its entire heightwhile the line 146 represents the profile of the finishformed tooth 147.The'profile of the tooth, preformed to its full height, was not shownbecause on the drawing this could not be clearly distinguished from thetooth profile 146. FIGS. 8 to 10 therefore disclose that, given a ratioof workpiece stroke to workpiece rotation of K 2, the teeth arepreformed with three enveloping planes to a tooth profile which is agood approximation to the tooth profile of the finished tooth form.

If preforming is to be preformed with more than three enveloping planes,the change gear set 78 is so selected that the number of workpiecestrokes for each tool rotation differs from K 2 but remains between K1.5 and K 2.5. The value of K is so selected that the same meshingposition between toolworm and workpiece is periodically repeated after afew teeth, depending on the desired number of enveloping planes, thenumber of said teeth having to be so selected that a multiple thereofdeviates by one tooth from the number of teeth of the workpiece wheel.

When gear-generating is performed over the entire height, the tool womis40 are retracted by a small amount by operating the control drive 61 inorder to reduce the pressure acting upon the workpiece. Furthermore, forfinish-forming, the dog clutch 92 in FIG. I is moved to the right toengage with the dogs on the gearwheel so that the planet wheel cage 97will then be rotated by the input shaft 88 of the differentialtransmission 77 via the gear drive 89, 90, the shaft 91, the change-gearsetand the pinion 96 so that the output shaft 98 of the differentialtransmission is provided with a supplementary rotation. The change-gearset 95 is previously so selected that the supplementary rotation of theoutput shaft of the differential transmission causes the ration K of thenumber'of strokes of the planes than in the preforming operation.

A displacement of the pivoting pin 33 of the doublearmed lever 18 toadapt the reciprocating speed of the tool slide in its right-hand motionto the changed rolling speed of the tool worms is not generallynecessary. The operating speed in preforming is so adjusted,

that the tip zone of the worm profile performs a pure rolling motionrelative to the workpiece because the principal rolling work inpreforming is performed by the tip zone of the worm thread of the toolworms. lf engagementof the additional rotation of the output shaft 98 ofthe differential transmission 77 increases the rotational speed of thetool worms while the tool slide 5 retains the same receiprocating speed,the zone of the worm thread profile in which a pure rolling motion isperformed will be displaced further inwardly relative to the toolwormsand into the pitch circle zone. However, this is desirable because infinish-forming the rolling work is distributed approximately unformlyover the entire height of the profile.

To produce a helical gear, a lead bush 11 with the appropriate drivercoller 14 is selected, the guide grooves 12 having a pitch angle .whichis nearest to the desired helix angle [3, said lead bush being mountedin the machine. The difference between thehelix angle 8 and the pitchangle of the guide grooves 12 is then adjusted, as described above, bythe adjusting worm 132 on the slotted link 131. The tool heads 42 withthe two tool worms 40 are also adjusted by their control drive 41, asshown in FIG. 11, so that the axis of the tool worms intersects theworkpiece axis X at an angle 7 which is obtained from the desired helixangle B of the gearing to be generated and the pitch angle of the toolworms.

Preforming and finish forming is then performed fundamentally in thesame manner as in the production of straight-toothed gear wheels.However, since the helix angle of the gear tooth system is measured onthe pitch circle and is greater on the tooth tip than on the pitchcircle, the tool-worms are appropriately adjusted to a somewhat largerangle at the beginning of the preforming operation, said angle beingprogressively reduced with progressive feed of tool worms 40 byoperating the coupled control drives 141 of the two tool heads 42 insteps of A-y until it corresponds tothe helix angle B of the geartoothsystem when the tool worms have fully penetrated.

lt isfound, particularly in the preformingot helical gearing and inparticular helical gearing having a large helix angle, that the toolworms 40 are displaced from the tooth direction at the beginning and endof each part-rolling operation. This isdue to the fact that they enterinto the workpiece andemerge therefrom at an angle and that,accordingly,at this-moment of time and tool worm can thrust on theworkpiece only in a tangential direction. To compensate for thiseffect,a correcting template 145 may be mounted von-the bracket of thespindle-bearing pedestal 40f the work slide 5, said bracket supportingthe slotted line 131. A follower dle of said lever being pivotablyjoined to the end of a lever 148 which in turn is mounted on the shaft137 which carries the eccentric pin 136 which functions as the bearingjournal for the double-armed lever 135. The piston rod of a piston 149is hinged on the left hand end of the lever 147 and the piston rod of apistonl50 is hinged on the right hand end of the said lever. in FIG. 1it is assumed that a changeover valve 151 is so adjusted that theunderside of the piston 149 and the top of the piston 150 are connectedto the oil pressure distribution network 49, and the oppositely-disposedsides of the pistons are connected to a return line 152 which extends toan oil sump.

The piston 149 bears at its upper end against an abutment so that theleft hand end of the lever 147 is able to pivot around a fixed point.The follower roller 146 disposed on the right nand end of the lever 147is constantly maintained in contact with the template 145 by virtue ofthe oil pressure acting on the top of the piston 150. Accordingly, thetemplate 145 ensures that during roller146 on one end of a lever 147(the right hand end in FIG-1) co-operates with the temp'late 145, themidthe reciprocating motion of the work slide the eccentric pin.137 ismoved up and down by means of the levers 147 and 148, and thedriving-worm 87, which rotates the work spindle 3, has an axialdisplacement imparted to it, said axial displacement being superimposedon the axial displacement provided by the slotted link 131 through thelever 135.The shape of the template 145 is so selected that the rotarymotion superimposed and imparted on the workpiece during the run in andrun out of the tool worms, rotates the workpiece opposite to the toolworms. The shape of the template is defined by virtue of trialgear-generating operations. If the action of the template 145 is to bediscontinued, which may be desirable in cold rolling of straight gearingor in finish-forming or at the end of finish-forming of helical gearing,the changeover valve 151 is moved into a second position in which oilpressure is applied to the top of the piston 149 and the underside ofthe piston 150 and the oppositely-disposed sides of the pistons areconnected to the return line 152. Accordingly, the left-hand piston 149is moved into its lower limiting position and the right-hand piston 150into its upper limiting position in the associated cylinders. Since themiddle of the lever 147 is pivotably joined to the end of the lever 148,the aforementioned action does not vary the position of the lever 148relative to its center position so that the eccentric pivoting pin 136for the double-armed lever retains its position when the action of thetemplate is discontinued.

If longitudinally-crowned gearing is to be produced, the disc cam 69,controlling the reciprocatingmotion of the wedge 52 for operating thetool slide 44 in the Y direction, is replaced by another disc cam which,as indicated by broken lines in FIG. 2, is slightly raised in the zonecorresponding to the inner dead center position of the tool slides.Accordingly, the said tool slides are retracted during each part-rollingoperation in the cetnral zone by an amount AY as indicated in FIG. 12 inwhich the path 153 of the tool worms relative tothe workpiece is shownwith a disc cam-69 corrected in the manner described hereinbefore.

The machine described hereinabove is also suitable for simultaneouslycold rolling more than one gearwheel. A disc cam 69, in which two raisedposition are provided in the zone corresponding to the inner deadcenterposition of the tool worms is used if the aforementionedgearwheels. are to be provided with longitudinal crowning, so that thepath 154, illustrated in FIG. 13, is obtained for the motion of the toolworms relative to the workpieces.

What we claim and desire to secure by Letters Patent is: t

1. in a method for cold rolling a gear tooth profile on thecircumference of a rotationally-driven cylindrical workpiece by means oftool worms having a reference profile, said tool worms being adapted toperform generating motions corresponding to the gear tooth profile to begenerated on the workpiece on a closedcircuit locus having locus havingone axis which is in the direction of and smaller than the tooth depthand which is substantially. smaller than another axis of said locuswhich is in the direction of the tooth length or thickness, theimprovement comprising the steps of effecting said rolling in aplurality of part-rolling operations, each part-rolling operation beingperformed over the entire workpiece width with the tool worms beingretained, at least over the tooth facewidth, in an inner dead centerposition in said locus, including preforming said tooth profile in anumber of enveloping planes by progressive feed toward the workpiece ofthe operating stroke of the tool worms in the radial direction of thetool worm and workpiece between successive complete movements in saidclosed-circuit locus, finish-forming said profile in a larger number ofenveloping planes, each enveloping plane being accomplished with thetool worms retained in a said dead center position.

2. A method according to claim 1, wherein each part-rolling operation isperformed with the profile of the tool worms in the same positionrelative to the workpiece so that the gear tooth profile is formed overits entire length in the same enveloping planes, each said envelopingplane having the same position relative to the tooth gaps being formed.

3. A method according to claim 2, wherein said preforming is perfonnedwith between 1.5 and 2.5 partrolling operations for each rotation of thetool worms, while finish-forming is performed with a ratio ofpartrolling operations for each rotation of the tool worms which differsfrom said preforming ratio by a small amount, said ratio being exactlydivisible into a figure no smaller than a high multiple of the number ofteeth of the workpiece.

4. A method according to claim 3, wherein when using two tool wor'insdiametrically opposed to each other relative to the workpiece, the wormthreads thereof are caused to act symmetrically relative to theworkpiece for eachpart-rolling operation, so that the torques acting onthe workpiece and resulting from the rolling pressure of the toolssubstantially cancel each other.

5. A method according to claim 1, for the cold rolling of helical gearteeth on the workpiece, wherein in preforming said helical gear teeth,thesetting angle of the tool worms relative to the workpiece angle isfirst set to a value larger than that corresponding to the helix angleand is then reduced in accordance with the associated reduction of theactual helix angle.

6. A method according to claim 1, wherein after preforming of the geartooth profile the feed of the radial stroke of the tool worms is reducedby a very small amount in order to reduce the rolling pressure forfinish-forming.

7. A method according to claim -1, wherein during the axial stroke ofthe tool worms a correcting motion is superimposed on the radial feed ofthe tool worms in order to obtain a longitudinally crowned tooth form.

8. ln a machine for cold rolling a gear tooth profile on thecircumference of a rotationally driven cylindri- I cal workpieceprovided with tool worms which are adjustable at an angle and aresupported in tool supports which are radially movable and axiallyreciprocable relative to the workpiece, and having a rotary drive forthe tool worms and for the workpiece to impart to both the tool wormsand the workpiece a relative generating motion which corresponds to theprofile to be generated, the improvement comprising means forreciprocating the tool supports exclusively in the direction which isradial relative to the workpiece axis, means for supporting theworkpiece in a work slide which can be reciprocated in parallel to theworkpiece axis over more than the facewidth of the gear teeth beingformed on the workpiece, and means for providing rotational drive of theworkpiece spindle through an interchangeable lead bush to produce thedesired rotation of the workpiece.

9. A machine according to claim 8, comprising a first,angularly-adjustable slotted link mounted on the work slide and adapted,during each stroke of the work slide, to axially displace a driving wormfor imparting rotation to the work spindle in order to counteractinherent generating action of the workpiece during each part-rollingmotion, and a second angularly-adjustable slotted link to axiallydisplace the tool worms during each stroke of the work slide in order tocounteract inherent generating action of the tool worms during eachpart-rolling motion.

10. A machine according to claim 8 comprising a crank together with acrank rocker, a connecting rod and a two-armed lever for reciprocatingthe work slide and so disposed'that the sinusoidal oscillation of thecrank rocker is converted into an axial reciprocation of the work slideso that the work slide moves ata constant velocity.

11. A machine according to claim l0, comprising a pin about which saiddouble-armed lever pivots, said pin being slidable to vary the length ofthe lever arms of the lever and therefore the length of the stroke andvelocity of the work slide.

12. A machine according to claim 8, comprising ainterchangeablecorrecting template mounted on the work slide and adaptedto impart, during each stroke of the work slide, an independent axialdisplacement to the driving worm for the rotational drive of the workspindle, said displacement being independent of the slotted link, inorder to influence the tooth direction resulting from the rollingoperation. 4 v

13. A machine according to claim 8, comprising a change gear set in therotational drive of the tool worms and of the workpiece for adjustingthe number of strokes of the work slide for each tool worm rotation.

14. A 'machine according to claim 8," wherein the rotational drive ofthetool worms and of the workpiece is provided with a differential drivehaving a planet wheel cage which can, by means of a changeover clutch,be optionally retained or be coupled with ya supplementary drive havinga change gear set.

1. In a method for cold rolling a gear tooth profile on thecircumference of a rotationally-driven cylindrical workpiece by means oftool worms having a reference profile, said tool worms being adapted toperform generating motions corresponding to the gear tooth profile to begenerated on the workpiece on a closedcircuit locus having locus havingone axis which is in the direction of and smaller than the tooth depthand which is substantially smaller than another axis of said locus whichis in the direction of the tooth length or thickness, the improvementcomprising the steps of effecting said rolling in a plurality ofpart-rolling operations, each part-rolling operation being performedover the entire workpiece width with the tool worms being retained, atleast over the tooth facewidth, in an inner dead center position in saIdlocus, including preforming said tooth profile in a number of envelopingplanes by progressive feed toward the workpiece of the operating strokeof the tool worms in the radial direction of the tool worm and workpiecebetween successive complete movements in said closed-circuit locus,finish-forming said profile in a larger number of enveloping planes,each enveloping plane being accomplished with the tool worms retained ina said dead center position.
 1. In a method for cold rolling a geartooth profile on the circumference of a rotationally-driven cylindricalworkpiece by means of tool worms having a reference profile, said toolworms being adapted to perform generating motions corresponding to thegear tooth profile to be generated on the workpiece on a closed-circuitlocus having locus having one axis which is in the direction of andsmaller than the tooth depth and which is substantially smaller thananother axis of said locus which is in the direction of the tooth lengthor thickness, the improvement comprising the steps of effecting saidrolling in a plurality of part-rolling operations, each part-rollingoperation being performed over the entire workpiece width with the toolworms being retained, at least over the tooth facewidth, in an innerdead center position in saId locus, including preforming said toothprofile in a number of enveloping planes by progressive feed toward theworkpiece of the operating stroke of the tool worms in the radialdirection of the tool worm and workpiece between successive completemovements in said closed-circuit locus, finish-forming said profile in alarger number of enveloping planes, each enveloping plane beingaccomplished with the tool worms retained in a said dead centerposition.
 2. A method according to claim 1, wherein each part-rollingoperation is performed with the profile of the tool worms in the sameposition relative to the workpiece so that the gear tooth profile isformed over its entire length in the same enveloping planes, each saidenveloping plane having the same position relative to the tooth gapsbeing formed.
 3. A method according to claim 2, wherein said preformingis performed with between 1.5 and 2.5 part-rolling operations for eachrotation of the tool worms, while finish-forming is performed with aratio of part-rolling operations for each rotation of the tool wormswhich differs from said preforming ratio by a small amount, said ratiobeing exactly divisible into a figure no smaller than a high multiple ofthe number of teeth of the workpiece.
 4. A method according to claim 3,wherein when using two tool worms diametrically opposed to each otherrelative to the workpiece, the worm threads thereof are caused to actsymmetrically relative to the workpiece for each part-rolling operation,so that the torques acting on the workpiece and resulting from therolling pressure of the tools substantially cancel each other.
 5. Amethod according to claim 1, for the cold rolling of helical gear teethon the workpiece, wherein in preforming said helical gear teeth, thesetting angle of the tool worms relative to the workpiece angle is firstset to a value larger than that corresponding to the helix angle and isthen reduced in accordance with the associated reduction of the actualhelix angle.
 6. A method according to claim 1, wherein after preformingof the gear tooth profile the feed of the radial stroke of the toolworms is reduced by a very small amount in order to reduce the rollingpressure for finish-forming.
 7. A method according to claim 1, whereinduring the axial stroke of the tool worms a correcting motion issuperimposed on the radial feed of the tool worms in order to obtain alongitudinally crowned tooth form.
 8. In a machine for cold rolling agear tooth profile on the circumference of a rotationally drivencylindrical workpiece provided with tool worms which are adjustable atan angle and are supported in tool supports which are radially movableand axially reciprocable relative to the workpiece, and having a rotarydrive for the tool worms and for the workpiece to impart to both thetool worms and the workpiece a relative generating motion whichcorresponds to the profile to be generated, the improvement comprisingmeans for reciprocating the tool supports exclusively in the directionwhich is radial relative to the workpiece axis, means for supporting theworkpiece in a work slide which can be reciprocated in parallel to theworkpiece axis over more than the facewidth of the gear teeth beingformed on the workpiece, and means for providing rotational drive of theworkpiece spindle through an interchangeable lead bush to produce thedesired rotation of the workpiece.
 9. A machine according to claim 8,comprising a first, angularly-adjustable slotted link mounted on thework slide and adapted, during each stroke of the work slide, to axiallydisplace a driving worm for imparting rotation to the work spindle inorder to counteract inherent generating action of the workpiece duringeach part-rolling motion, and a second angularly-adjustable slotted linkto axially displace the tool worms during each stroke of the work slidein order to counteract inherent generating action of the tool wormsduring each part-rolling motion.
 10. A machine according to claim 8comprising a crank together with a crank rocker, a connecting rod and atwo-armed lever for reciprocating the work slide and so disposed thatthe sinusoidal oscillation of the crank rocker is converted into anaxial reciprocation of the work slide so that the work slide moves at aconstant velocity.
 11. A machine according to claim 10, comprising a pinabout which said double-armed lever pivots, said pin being slidable tovary the length of the lever arms of the lever and therefore the lengthof the stroke and velocity of the work slide.
 12. A machine according toclaim 8, comprising an interchangeable correcting template mounted onthe work slide and adapted to impart, during each stroke of the workslide, an independent axial displacement to the driving worm for therotational drive of the work spindle, said displacement beingindependent of the slotted link, in order to influence the toothdirection resulting from the rolling operation.
 13. A machine accordingto claim 8, comprising a change gear set in the rotational drive of thetool worms and of the workpiece for adjusting the number of strokes ofthe work slide for each tool worm rotation.